To prevent tire cord strike-through, a condition wherein the reinforcing tire cord penetrates the innerliner layer, leading to air leakage and tire failure, it is a common practice to add a buffer layer between the carcass layer containing textile or steel cords and the innerliner layer. This buffer layer has been referred to as tie gum, tie layer, cushion compound, or liner backing layer and typically includes blends of natural rubber (NR) and styrene-butadiene rubber (SBR). For purposes of the present invention, this tire component is referred to as the “tie layer.” Typically, the composition of the tie layer is similar to the composition of the carcass compound in order to provide the necessary building tack for maintaining a coherent tire structure in the uncured, or “green,” state, cured adhesion, and satisfactory dynamic properties during tire use. However, both NR and SBR are highly permeable rubbers. Consequently, a thicker cross-section would be required in order to reduce air permeability though this layer and so maintain tire pressure. In order to achieve overall weight reduction in a tire by using a thin, highly impermeable innerliner, it is necessary to find a means of reducing the cross-sectional thickness of the tie layer. The present invention provides a solution by using at least one highly impermeable isobutylene-based elastomer in combination with, for example, NR in the tie layer; particularly preferred impermeable elastomers being brominated isobutylene-paramethylstyrene copolymers (BIMS). The present invention is useful in tires employing conventional innerliner compositions based on halogenated isobutylene-containing elastomer components as well as thermoplastic elastomeric tire innerliner compositions based on vulcanized blends of engineering resins, e.g., polyamides and BIMS, produced, for example, using dynamic vulcanization, as disclosed in EP 0 722 850 B1. Consequently, the present invention provides a tie layer suitable for joining a layer based on a dynamically vulcanized alloy of polyamide and a brominated copolymer of isobutylene-para-methylstyrene, such as an innerliner composition, to a tire carcass without impairing the improved permeability characteristics achieved by the innerliner. It is also useful in other applications in which an air or fluid holding layer is used in combination with another layer, particularly where the other layer includes reinforcing fibers or cords, e.g., hoses and other vessels required to retain a gas or a fluid.
U.S. Pat. No. 5,738,158 discloses a pneumatic tire having an air permeation prevention layer or innerliner layer composed of a thin film of a resin composition including at least 20% by weight of a thermoplastic polyester elastomer comprised of a block copolymer of polybutylene terephthalate and polyoxyalkylene diimide diacid at a weight ratio of polybutylene terephthalate/polyoxyalkylene diimide diacid of 85/15 or less. The resin composition can further include dispersed rubber particles wherein the rubber particles have been dynamically vulcanized. The concept of using a resin composition as an innerliner layer has been further developed by various inventors of the same assignee, see, e.g., U.S. Pat. No. 6,079,465, which claims a pneumatic tire that incorporates such an innerliner and discloses the use of various thermoplastic resins for use in the composition. This patent also discloses the presence of a tie layer and another layer to promote bond or adhesive strength of the innerliner layer in the overall structure. The further development of this technology to improve adhesion of the innerliner layer in the structure is described in U.S. Pat. No. 6,062,283 wherein melt viscosities and solubility parameters of thermoplastic resin components and elastomer components are controlled according to a specific mathematical formula.
Published application U.S. 2002/0066512 discloses a pneumatic tire comprising a carcass comprising a ply of cords defining the innermost reinforcing cord layer extending between bead portions, and an airtight layer disposed inside the cords of the carcass ply along the inner surface of the tire, covering the substantially entire inner surface of the tire, wherein the airtight layer is made of air-impermeable rubber including at least 10 weight % of halogenated butyl rubber and/or halogenated isobutylene-paramethyl styrene copolymer in its rubber base, and a thickness of the airtight layer measured from the inner surface of the tire to the cords of the carcass ply is in a range of from 0.2 to 0.7 mm. The publication also discloses that the “airtight layer,” defined by a rubber layer between the tire inner surface and the innermost tire cords or carcass cords, can be a double layer comprising an inner layer of an air-impermeable rubber compound and an outer layer of a diene-based rubber which is not air-impermeable. Alternatively, the outer layer may be of the same air-impermeable rubber compound or a similar air-impermeable rubber compound, which compound is further described in the publication as including halogenated butyl rubber and/or halogenated isobutylene-paramethyl styrene copolymer and diene rubber as well as carbon black (see paragraphs 28-34).
Other references of interest include: WO 2004/081107, WO 2004/081106, WO 2004/081108, WO 2004/081116, WO 2004/081099, JP 2000238188, EP 01 424 219, U.S. Pat. No. 6,759,136, and U.S. Pat. No. 6,079,465.